my alternator only charges when it feels like it, so I often end up with dead battery

Asked by Deville1998 May 10, 2017 at 07:08 PM
about the 1998 Cadillac DeVille

Question type: Maintenance & Repair

my alternator "sometimes" start charging 3 minutes after the engine has started and sometimes it won't charge at all. And, when it charges, it might stop charging for no reason and I end up with dead battery on side of the road, why?

3 Answers

That was my first idea so I got the alternator tested and came
out GOOD. On the alternator, apart from the BTTY terminal,
there is 2 other wire hooked up to the regulator. To narrow down
my search, I've compared what reading I was getting out of the
female adapter on my GM Truck and when the switch is on, the L
terminal gives me the same voltage as the car btty. But, on my
cadillac, I get only half the voltage +/- 5.5 VDC. Since I've got
the charging schematic, I can see that the L terminal goes to the
voltmeter (light) then ignition. So, why only half the voltage I
should get? And also, can someone explain how the regulator
gets excited in order for the alternator to start charging the btty?
This is an intermittent problem so which part in the system could
be on or off depending on the alternator ghost wishes?

taver91, Thanks for your reply but the regulator is not separate
and, as I wrote, I had the alternator tested and turned out good.
I'm 98% sure the problem lies with a component that tell the
regulator to start charging because, as I wrote, with the switch
ON, on the L terminal, I'm getting only half the voltage of the
battery compare to the reading I get from the L terminal on my
GM truck with the switch ON. I know there not the same vehicles
and same alternator but there must be something consistent with
the way "regulator gets excited and drives the alternator to
charge" . That is the information I'd like to know and maybe I
could bypass the faulty component and confirm my theory. So,
can someone explain to me how the regulator gets excited and
drives the alternator to start / stop charging?

First thing is when I'm driving it and slow down to make a turn or to stop it will just die on me and I'll have to restart it. Second - Before it does this, while pushing on the gas it will cut out of...

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